The present invention relates to an arrayed waveguide grating type optical multiplexer/demultiplexer used in at least either one of the optical multiplexer, the optical demultiplexer or the optical multiplexer/demultiplexer.
In recent years, in the field of optical communications, research and development in wavelength division multiplexing (WDM) transmission systems as a method for increasing the transmission capacity drastically has been actively pursued and the practical application is now advancing. The wavelength division multiplexing transmission systems performs wavelength division multiplexing for transmission, for example, a plurality of lights each having a different wavelength from each other. In such wavelength division multiplexing transmission systems, an optical multiplexer/demultiplexer is required for demultiplexing a plurality of lights each having a different wavelength from each other from the light which has undergone wavelength division multiplexing or for multiplexing a plurality of lights each having a different wavelength from each other.
As an example of the optical multiplexer/demultiplexer, an arrayed waveguide grating (AWG) type optical multiplexer/demultiplexer is known. The arrayed waveguide grating type optical multiplexer/demultiplexer is composed by forming on a substrate 11 an optical waveguide unit 10 having a waveguide such as shown for example in FIG. 7A.
The waveguide construction of the arrayed waveguide grating type optical multiplexer/demultiplexer comprises one or more optical input waveguides 12 arranged side by side, a first slab waveguide 13 connected to the output ends of the optical input waveguides 12, an arrayed waveguide 14 connected to the output end of the first slab waveguide 13, a second slab waveguide 15 connected to the output end of the arrayed waveguide 14, a plurality of optical output waveguides 16 connected to the output end of the second slab waveguide 15 arranged side by side. And the arrayed waveguide 14 consists of a plurality of channel waveguides 14a arranged side by side.
Each of the aforementioned channel waveguides 14a, which propagates the light outputted from the first slab waveguide 13, is formed of a predetermined different length from each other.
The optical input waveguide 12 or the optical output waveguide 16 is, for example, provided corresponding to the number of the signal lights each having a different wavelength from each other, for example, demultiplexed by arrayed waveguide grating type optical multiplexer/demultiplexer. The channel waveguides 14a are generally provided so many as for example 100 waveguides. But for the purpose of simple illustration the number of the waveguides of each waveguide 12, 14a, 16 is shown informally in FIG. 7A. In addition, the arrayed waveguide grating type optical multiplexer/demultiplexer is formed approximately symmetrical with respect to the broken line C in the drawing.
FIG. 7B shows the enlarged schematic view within the frame A depicted by dotted line in FIG. 7A. As shown in this figure, in the conventional arrayed waveguide grating type optical multiplexer/demultiplexer, the output ends of the optical input waveguides 12 of a rather curved shapes are directly connected to the input side of the first slab waveguide 13. In addition, the input ends of the optical output waveguides 16 of rather curved shapes are directly connected to the output side of the second slab waveguide 15 likewise.
The optical input waveguides 12 are, for example, connected to the optical fibers of the transmitting side so that the light which has undergone wavelength division multiplexing can be introduced therein. The light introduced to the first slab waveguide 13 through one of the optical input waveguides 12 is diffracted by means of the diffraction effect, inputs into each of the plurality of channel waveguids 14a and propagates through the arrayed waveguide 14.
The light propagating through the arrayed waveguide 14 reaches the second slab waveguide 15 and further condensed into the optical output waveguide 16 thereby being outputted. As the length of each channel waveguide 14a differs with each other by a predetermined length, a phase shift is generated in each light after having propagated through each channel waveguide 14a and so the phasefront of the lights inclines corresponding to the predetermined length. As the condensing position of the light is determined in accordance with the angle of the inclination, the condensing position of the light having different wavelength differs with each other. Hence, by forming the optical output waveguide 16 at the condensing position of the light of each wavelength, it is made possible to output lights each having a different wavelength from each other by a predetermined design wavelength spacing from the respective optical output waveguide 16 corresponding to each wavelength.
For example as shown in FIG. 7A, when the light which has undergone wavelength division multiplexing having a different wavelength xcex1, xcex2, xcex3 . . . xcexn (n is a integer more than 1) from each other by a predetermined design wavelength spacing is inputted from one optical input waveguide 12, the light is diffracted by the first slab waveguide 13 and reaches the arrayed waveguide 14. Then, it propagates further through the arrayed waveguide 14 and slab waveguide 15 and condenses as described above to the different positions depending on their wavelengths thereby the lights having the different wavelengths input into the optical output waveguides 16 respectively. Further, they propagate through the respective optical output waveguides 16 and outputted from output end of the optical output waveguides 16. By connecting an optical fibers to the output ends of each optical output waveguide 16, the aforementioned lights of each wavelength can be taken out through the optical fiber.
In addition, as the arrayed waveguide grating makes use of the light reciprocal (reversibility) principle, it has not only a function as an optical demultiplexer but also has a function as an optical multiplexer. In other words, in case of inputting a plurality of different lights each having a different wavelength from each other by a predetermined wavelength from respective optical output waveguide 16 corresponding to each wavelength, to the contrary as shown in FIG. 7A, these lights are multiplexed through the propagating path reverse to the aforementioned path so that a light having the different wavelengths is outputted from the single optical input waveguide 12.
In this arrayed waveguide grating type optical multiplexer/demultiplexer, the improvement in the wavelength resolution of the arrayed waveguide grating is proportional to the different length (xcex94L) between the adjacent channel waveguides 14a composing the arrayed waveguide grating. Consequently, by designing xcex94L a greater value, an optical multiplex/demultiplex of a light which has undergone wavelength division multiplexing having a narrow wavelength spacing becomes possible which the conventional optical multiplexer/demultiplexer could hardly realize. For example, by designing xcex94L a greater value thereby the design wavelength spacing for multiplexing or demultiplexing equals to or less than 1 nm, a multiplex/demultiplex function of a plurality of light signals having a wavelength spacing of 1 nm or less can be achieved so that the optical multiplex/demultiplex function of a plurality of lights required for the realization of a high density wavelength division multiplexing communications can be accomplished.
The arrayed waveguide grating type optical multiplexer/demultiplexer according to the present invention comprises one or more optical input waveguide arranged side by side, a first slab waveguide connected to the output ends of the optical input waveguides, an arrayed waveguide connected to the output end of the first slab waveguide and consisted of a plurality of channel waveguides arranged side by side each having a different length from each other by a predetermined size, a second slab waveguide connected to the output end of the arrayed waveguide, a plurality of optical output waveguides arranged side by side connected to the output end of the second slab waveguide. This arrayed waveguide grating type optical multiplexer/demultiplexer has a demultiplex function to demultiplex the light having a plurality of wavelengths different from each other by a predetermined design wavelength spacing into a plurality of lights each having a different wavelength from each other, and a multiplex function to multiplex a plurality of lights each having a wavelengths different from each other by said predetermined design wavelength spacing, and during optical demultiplexing, a light having a plurality of different wavelengths from each other, an integral multiple spacing of said predetermined design wavelength spacing, is inputted into the optical input waveguide of the arrayed waveguide grating type optical multiplexer/demultiplexer and a plurality of lights each having a wavelength different from each other are demultiplexed to be outputted from the optical output waveguide side, and during optical multiplexing, lights each having a different wavelength from each other by a wavelength spacing, an integral multiple spacing of said predetermined design wavelength spacing are inputted into the optical output waveguides of the arrayed waveguide grating type optical multiplexer/demultiplexer and the light of each wavelength is multiplexed to be outputted from the optical input waveguide side, wherein an approximately rectangular optical amplitude distribution forming waveguide is connected between at least either one of one or more optical input waveguides and one or more optical output waveguides and a slab waveguide as the connection couple, and the approximately rectangular optical amplitude distribution forming waveguide changes the optical amplitude distribution of the light propagating from the optical input waveguide side or the optical output waveguide side to the corresponding slab waveguide side from a Gaussian shape to an approximately rectangular shape.